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We propose a five year program, in which we will develop the next generation ofbeam instrumentation necessary to operate future accelerators

with high current, lowemittance and high repetition rate.

RF beam position monitors is one

of the detectorsto be developed

in order to measure the length of very short electron bunches (r.m.s. ≤1ps). In addition, we will use these new and/or improved techniques to instrument thefacility needed to validate

the CLICdesign forthe high current drive beam

that will bedecelerated asRF poweris

extracted to

accelerate

a parallel

beams withunprecedented

highgradients, that

is 150 eV/m. This will allow us to built multi-TeVmachines.

This facility has to beoperational by 2008, and final results available by2010in orderto meet the scheduleimposedby ….

2.

INTRODUCTION

1.Vision of the future

2.Funding Agencies meeting

3.Expertice of the group

3.

DESCRIPTION OF CLICAND CTF3

As explained above, our group is very interested on the physics capabilities of ahigh luminosity (1034-1035/cm2/s)Multi-TeV e+e-

collider, and we are of the opinionthat the ultimate machine design to achieve this goal will be based on theso-called“Two-Beam Scheme”

from CLIC, Compact LInear Collider, currently underdevelopment at CERN.

The CLIC design aims for a maximum energy of 3 to 5 TeV (centre of mass) to bereached by acceleration with high gradients of 150 MV/m at 30 GHz with a RF pulselength of 130 ns.

In the two-beam scheme, the pulsed RF power (460 MW per metrelength of linac) to feed the accelerating structures is produced byextracting 30 GHzpowerfrom high-intensity/low-energy drive beams running parallel to the main beam.These drive beams are generated in a centrally-located area and then distributed alongthe main linac. The beams are accelerated using a low frequency (937 MHz) fully-loaded normal-conducting linac. Operating the linac in the fully-loaded conditionresults in a very high RF-power-to-beam efficiency (~97%). Funnelling techniques incombiner rings are then used to give the beams the desired bunch structurewith theconcomitant increase in intensity, in this process the bunch spacing is reduced instages from 64 cm to 2 cm, and the beam current is increased from 7.5 to 240 A.TheRF power is extracted from the drive beam in Power Extraction and TransferStructures (PETS).

An overall

CLIC

layout of the complex is shown in Fig.1. A single tunnel, housingonly the two linacs and the various beam transfer lines, results in a very simple, costeffective and easily extendable configuration for energy upgrades.

Fig. 1: Overall layout of the CLIC complex.

The technical feasibility of two-beam acceleration has been demonstrated in CLICTest Facility 2 (CTF2). In this test, the energy of a single electron bunch was increasedby 60 MeV using a string of 30 GHz accelerating cavities powered by a high intensitydrive linac. Peak accelerating gradients of 190 MV/m have been obtained in CTF2using molybdenum-irises in 30 GHz copper structures with rf pulse lengths of 16 ns.This result has to be confirmed for the nominal CLIC pulse length (130 ns).

Anexperimental demonstration of the principle of the bunch combination scheme hasbeen made at low charge using a modified layout of the former LEP Pre-Injector (LPI)complex.

A number of CLIC specific items that need to be

understood have been listed by theInternational Technical Review Committee. For the

so-called R1 items we needtoprovide a feasibility proof, while the

R2 items

are thosewhich must be investigatedin order to arrive at a Conceptual Design.

the validation of the drive-beam generation scheme with a fully-loaded linac(R1.2), and the design and test of an adequately damped power-extractionstructure, which can be switched ON and OFF (R1.3), requires the complexwith the delay loop andthe combiner ring (location 2);



the validation of beam stability and losses in the drive-beam decelerator, anddesign of a machine protection system (R2.1), and the test of a relevant linacsub-unit with beam (R2.2), requires theCTF3-CLEX experimental area, whichconsists of a high-power test stand (location 3), the Test Beam Line (TBL)(location 4) and the probe beam with a relevant linac two-beam module(location 5).

be monitored all along the linac inorder to keep the radiation level and the activation as low as possible.

We have takenadvantage of our expertise on beam instrumentation, and taken theresponsibility

for

theBeamLossMonitor (BLM)

system for the linac.The linac, providing a 3.5A,1.5s electron beam pulse of 150MeV, is scheduled for completion by the end of2004, and our detector will be completely installed by then.The goal of our effort is toprovidequantitative beam loss measurements

with a BLM system that willbe able todetect losses corresponding to the ‰level of the nominal beam current.An intensivesimulation work has beencarried out

based onGeant3.21

in order to predict

thecharacteristics of theelectromagnetic

showers in a realistic accelerator environment.The simulation takes into account that the CTF3 linac is

composed of acceleratingmodules that have a beam position and an intensity monitor followed by a set of threequadrupoles and two 3 GHz accelerating cavities. Each module is 4m long and thereare a total of 9 consecutives modules along the linac.

The layout of a linac moduleequipped with beam loss monitors is shown in Figure 1.

Figure 1:

(a)

Layout of the beam

loss system in a CTF3 linac module

and monitoringchamber. (b)Geometry simulated by Geant3.21.

Asshown in Fig. 2, using the

full geometry and beam description we expected

thata‰

loss of the beam requires a BLM system based on detectors capable ofmeasuring1010

to 1012

particles/cm2/s[i]. In parallel to the simulations,

a preliminary test of beamloss monitoring was performed in November 2003 [ii] on the already existing part ofthe accelerator.

From that exercise we learn that detectors based on secondaryemission are fast enough to see the time structure of the beam, and that the detectorthat we had developed to monitor high flux hadron beams as those expected at highpower proton drivers and neutrino factories, could be used.

Based on this

simulationsand cost considerations, it was decided

to build a system with 4detectors per module.

Figure 2: Electrons / Positrons flux distribution at 100cm from the point of the beamloss in the X/Y plane transverse to the beam line.

The individual

detectors aresmall gas sealed ceramic chamber sensitive to chargedparticles and developed by Northwestern University, Fermilab andRichardsonElectronics. It hasboth a very good resistance to radiation and a high dynamic range(>105). The chamber canbe filled with helium andbeused as an ionization chamber(IC), or just under vacuum andbeused as a Secondary Electron Monitor chamber(SEM). Preliminarytest made at the Fermilab booster

abort area,

shows

that asexpected,the response of the IC chambers will saturate around1010particles/cm2/s,while the SEM continues to have a linear response even at high flux rate, see Fig. 3.

The choice between anIC or a SEM will be a

compromise between the timeresolution, which is faster for the SEM mode, and the sensitivity, which is 1000 higherfor the IC

mode. The output signal is amplified near the detector itself. Dataacquisition, based on 50MHz ADC’s is performed in a gallery, located just above theaccelerator tunnel.

The mechanical support for the detectors allows an easymodifications of their longitudinal

and transverse

positions depending on theexperimental needs.

The experience that we will acquire will be needed for the design of the beam lossmonitor system of the R2.1-TBL project.

The goalof the Test Beam Line (TBL) isto demonstrate the feasibility of the CLICdrive beam decelerators[1]

at CTF3. The main concerns are whether or not this beamcan be operated with acceptable beam losses and sufficient beam stability.

Asalready mentioned, these concerns

were classified

as a

R2 feasibility itemforCLICtechnology in

the International Linear Collider–

Technical Review Committee(ILC-TRC) report [2]:

“The very high power of the drive beam and its stability are serious concerns forCLIC. The drive beam stability should be validated, and the

drive beam MachineProtection

System, which is likely to be a complex system, should be designed toprotect the

decelerator structures”

The TBL will be a scaled model of a CLIC drive beamdecelerator that will allow us totest the operation procedure,therequired instrumentation andthefeedback systems forsuch a decelerator in order to guarantee the stability of the beam.In addition, the TBLwill be

used to benchmark the predictive power of

the

numerical simulation toolwhich are used for its design.

The

potential difficulties are due to:



the very high current of beam (damage potential),



the large total energy spread (up to 90%), and



the presence of considerable transverse wakefields.

In addition, the characteristics of this beam are very different from

any otherbeam

previously build. Therefore,this facility will also allow us

to gain experience on theconstruction and installation procedure.

DESCRIPTION OF THE TBL

The TBL will be20 m long

scaled model of theCLIC drive beam decelerator sectorto be

located at the end of CLEX, see Fig. 1. Table 1 gives a comparison of theparameters for the drive beam of the CLIC and at the TBL. As shown, the beamenergy and the beamcurrent are a factor of 13 and4.3 lower compared with a CLICdecelerator. The FODO period length is the same as for CLIC, but the total length isabout 30 times smaller than a CLIC decelerator sector.

TBL tentative parameters ?comparison with CLIC decelerator

20

2.23

35

0.15

TBL

624

Total length (m)

2.23

FODO period length (m)

147

Beam current (A)

2

Beam energy GeV

CLIC

A tentative layout of the TBL is shown in Fig. 2. Here we assumethat there will

7FODO modules, which is the minimum numberrequired to performawell thought-outtests of the drive beam tuning procedures. In addition, there will be 10-16 RF power-extracting structures (PETS).

Each TBL module corresponds to one full FODO cell equipped with:



two quadrupoles (includingmovers for steering),



two PETS (provided by WP7 along with the

power measurement and RFload, and corresponding monitoring),



two BPM’s,



appropriate monitors for beam loss.

The PETS girders and the quadrupole supports have motors for independent remotecontrol of their transverse position. The quadrupole currents are individuallycontrolled and the quadrupole

strength should be sufficient for a phase advance perFODO cell of up to 1200

with a 300 MeV beam (the maximum beam energy availablefrom the drive beam accelerator and combiner ring with

minimum beam current).

D

F

D

F

D

F

D

F

D

F

D

F

D

F

D

F

DUMP

DUMP

35 A,150MeV

beam from

combinerring

Instrumentationsection

Decelerator FODOmodules

D

F

PETS

BPM

PETS

BPM

2.23m

20 m

An instrumentation section at the end of the TBL will allow us to determined themean energy, the energy spread and the emittance growth of the beam after passagethough the TBL. All the beam instrumentation needs to be capable to make a timeresolvedmeasurements with a resolution of at least 10

nsin order to observe the buildup of the instabilities along the 140 ns long bunch train.

Sophisticated software for automated steering and position feedback has to bedeveloped in close collaboration with the team working on the CLIC deceleratordesign, to mimic with the TBL the tuning and operation procedures foreseen forCLIC.

PURPOSE, OPERATION PRINCIPLE, AND DEVELOPMENT REQUIRED FOREACH SUBDETECTOR SYSTEM